The present invention relates to noise silencing panels for vehicles and more particularly relates to such panels as are used to silence the noise generated by engine cooling fans.
Typically, a fan generates low frequency noise related to the blades passage and its harmonics and high frequency broad band aerodynamic noise. Conventional designs for silencing fan noise have included a plurality of spaced sound absorbing units or baffles comprising perforated casings filled with sound absorbing material. An example of such a structure is disclosed in U.S. Pat. No. 3,897,850 granted to Thompson et al on Aug. 5, 1975. While structures of this sort do attenuate noise in the mid to high frequency range, they are not particularly effective in attenuating noise in the low frequency range.